基于前向纠错的自适应网络传输机制

针对无线网络中的传输控制协议(TCP)因为丢包触发丢包重传机制而导致传输性能大幅下降的问题,提出了一种基于前向纠错的自适应传输机制(AdaptiveFEC).该机制通过前向纠错来减少数据段的丢失,以避免触发TCP的丢包重传机制,从而达到提升TCP传输性能的目的.首先,根据当前的网络状况以及当前连接的数据传输特征确定当前...     

一种改进的高速链路前向纠错编码

在高速链路的可靠传输中,物理层前向纠错的研究主要集中在提高编码的纠错性能,且编码冗余位全部用于纠错校验,难以满足用户在传输中加载定制信息的应用需求。针对这一问题,设计了一种编码利用率更高、灵活性更强的前向纠错编码方案,并通过Matlab和综合工具对性能和开销进行了评估,在不损失编码性能的前提下得到了一系列可以无损加载用户定制信息的前向纠错编码。     

确认平滑:一种改善无线链路上的TCP性能的实现

许多研究者已经发现，在无线链路上使用链路层自动请求重传(ARQ)来恢复无线链路差错，会在无线链路上和TCP源端产生大量的突发性流，从而使路由器拥塞，导致分组丢失和吞吐量下降．本文提出了一种解决方案，在ARQ的接收端，利用漏桶对接收确认分组进行平滑，使分组的发送能保持一定的间隔．仿真结果表明，平滑能提供更好的吞吐量性能和更低的丢失率。     

前向纠错编码在网络传输协议中的应用综述

前向纠错编码是一种在网络传输中应对丢包的技术.在传输过程中加入冗余数据,使接收端在丢包场景下可通过冗余数据直接恢复出原始数据.在丢包多、时延大的场景下,适当加入前向纠错编码可以大量节省超时重传的等待时间,从而提高网络传输的服务质量.过多地添加冗余会造成带宽的浪费,而过少地添加冗余会导致服务器端接收到的数据不足以恢复在传...     

ATM网多媒体业务传输中的前向纠错研究

与传统的闭环纠错技术相比 ,前向纠错技术 (FEC)更适用于 ATM网多媒体业务传输 .本文对几种主要的FEC机制进行了定性分析 ,得到了评价其性能的参数并进行了比较 ;深入探讨了纠错所在层次的问题 ,对信元级 FEC和包级FEC的性能进行了分析和比较 ,得到了一些重要结论 .本文的研究对 ATM网多媒体业务传输研究具有指导意义     

一种自适应的视频流化前向纠错算法

网络视频应用经常会受到数据包丢失或错误以及网络带宽资源不足的干扰.相关研究表明:在多数情况下,动态变化的网络带宽和丢包率是影响视频流化质量的关键因素.因此,为了保证视频质量,可以采用前向纠错(forward error correction,简称FEC)编码来提高视频数据传输的可靠性;同时,为了适应网络状态的变化,发送端可以调节视频数据的发送速率,并在视频源数据与FEC数据之间合理分配网络传输带宽.首先通过对视频流结构的分析,在充分考虑帧之间的依赖关系和帧类型的基础上提出了一种帧的解码模型.在此基础上,建立了用于在视频源数据和FEC数据之间分配网络带宽资源的优化算法.实验表明,该模型可以有效地适应网络状态的变化,并通过优化分配网络带宽资源来使接收端获得最大的可播放帧率.     

组播环境中层式前向纠错与TCP友好拥塞控制策略研究

该文详细描述了组播环境中基于层式结构的前向纠错和基于接收端驱动的TCP友好拥塞控制策略，采用层式结构发送数据可以满足尽量多的异构接收用户，不同的用户可以根据网络状态和计算的TC宏好发送速率选择接收不同的数据层和纠错层的数据流。采用接收端驱动和接收端计算包往返时间的方法可以有效地防止大量的反馈信息和计算阻塞发送端。实验和分析均证明该策略工作良好。     

实时视频通信中的自适应前向纠错方案设计

本文针对实时视频通信中的网络丢包问题,提出了一种基于Reed Solomon算法的自适应FEC方案。与以往的静态FEC编解码方案不同,该方案引入一种新的基于SIP／RTP的QoS反馈机制,根据丢包率大小在发送端调整FEC冗余度、整体发送速率以及封包大小来保证服务质量;并针对网络突发丢包情况,在对数据包进行FEC编码时采用了交织技术     

基于TCP友好速率控制和前向纠错的MPEG-2视频传输

针对Internet视频传输面临拥塞控制和数据包丢失的问题，结合TCP友好的速率控制算法和前向纠错机制建立视频传输的分层体系构架和控制策略。传输体系同时采用以GOP为基本分析单元的视频帧速率预测模型，实现根据网络丢包率的变化动态地优化配置前向纠错的冗余信息。实验证明，传输体系采用动态优化的前向纠错能实时地适应带宽的变化，有效地降低数据包丢失带来的影响，从而改善视频回放质量。     

基于优化前向纠错和TCP友好阻塞控制的实时音频传输策略研究

结合优化前向纠错策略和TCP友好阻塞控制算法，提出了一个新的基于Internet的实时音频数据传输策略．该策略根据TCP友好阻塞控制算法计算实时音频数据流在网络上可以获得的TCP友好的传送速率，同时根据检测到的网络状态和计算的速率，利用优化前向纠错策略来计算在发送端的数据包中应该包括多少冗余信息、采用何种编码方法才能在接收端获得最好的服务质量．实际的Internet实验和在内部网络的模拟实验显示该策略工作良好。     

Analysis of link-level hybrid FEC/ARQ-SR for wireless links and long-lived TCP traffic

Since the TCP protocol uses the loss of packets as an indication of network congestion, its performance degrades over wireless links, which are characterized by a high bit error rate. Different solutions have been proposed to improve the performance of TCP over wireless links, the most promising one being the use of a hybrid model at the link level combining Forward Error Correction (FEC), Automatic Repeat Request with Selective Repeat (ARQ-SR), and an in-order delivery of packets to IP. The drawback of FEC is that it consumes some extra bandwidth to transmit the redundant information. ARQ-SR consumes extra bandwidth only when packets are lost, its drawback is that it increases the round-trip time (RTT), which may deteriorate the performance of TCP. Another drawback of ARQ-SR is that a complete packet can be retransmitted to correct a small piece of errored data. We study in this paper the performance of TCP over a wireless link implementing hybrid FEC/ARQ-SQ. The study is done by simulating and modeling long-lived TCP transfers over wireless links showing Bernoulli errors. We are motivated by how to tune link-level error recovery, e.g. amount of FEC, persistency of ARQ, so as to maximize the performance of TCP. We provide results for different physical characteristics of the wireless link (delay, error rate) and for different traffic loads (number of TCP connections).     

基于RTT自适应的无线TCP改进算法

针对TCP Reno在无线环境下的性能恶化问题,在研究分析TCP Reno拥塞控制算法问题的基础上,提出一种基于RTT自适应的改进算法.该算法实现了丢包区分的拥塞窗口与慢启动门限调整,减轻了传统TCP由于无法区分拥塞丢包与误码丢包、盲目将拥塞窗口减半带来的性能下降.分析了该算法的可行性,并通过NS仿真对其吞吐量、带宽利用率、公平性等指标进行评估.仿真结果表明,相对TCP Reno,改进算法实现了无线环境下的TCP性能改善,同时具有一定的友好性与公平性.     

一种自适应改进无线TCP性能的算法

对采用TCP协议传输数据的实现过程及其在无线网络中可能遇到的问题进行了描述，针对这些问题提出了一种算法对无线链路下一时刻的误码率进行了估计，根据这个估计对TCP进行了修改以自适应选取合适的TCP报文段尺寸来传输数据。在网络仿真器（NS2）中仿真一个误码率时变的无线信道，把修改后的TCP置于NS仿真环境中进行仿真，实验结果表明了该改进方法有效。     

Improving TCP performance over wired–wireless networks

Today there is a growing demand for Internet services over WLAN hotspots. Majority of the Internet services today are based on TCP. However, TCP is not well-suited for heterogeneous networks consisting of wired and wireless networks. Losses in wireless network, which are quite frequent, are often misinterpreted by the TCP sender as loss due to congestion, which leads to poor performance of TCP. Hence, it is important to shield the TCP sender from wireless error. In this paper, we propose an improved method for identifying cases of wireless losses and tackling the loss at the local link level through MAC layer retransmissions. We then evaluate the effect of MAC layer retransmissions on the performance of TCP both analytically and empirically. Our empirical results show that significant improvement in TCP performance is possible through MAC layer retransmission.     

一种无线实时流媒体增强型自适应FEC控制机制

无线网络动态的信道特性和带宽有限等特点,使得在无线环境下为流媒体应用提供QoS保证面临更大的挑战。提出一种用于无线实时流媒体传输的增强型自适应前向纠错控制策略,以提高接收方的播放质量。该策略采用跨层设计的方法,根据当前的网络状态,自适应地调整MPEG视频帧的发送速率,在视频源数据和冗余数据之间动态分配网络带宽。仿真结果表明,该策略能使接收方获得最大的可播放帧率,有效提高流媒体传输的可靠性和实时性。     

An ENA algorithm to enhance the performance of TCP over satellite links

Reliable Transport protocols, such as TCP, are tuned to perform well in terrestrial networks where most segment losses occur because of congestion. However, networks that involve satellite links also suffer from significant losses that are because of bit errors. TCP responds to all losses that are because of bit errors. TCP responds to all losses by invoking congestion control and avoidance algorithms, which result in degraded performance when using a satellite link.In this paper, we propose an Error Notification ACK (ENA) algorithm that distinguishes error segments from losses due to network congestion. We also propose a method for implementation of the algorithm and evaluate the performance of the Tahoe, Reno and SACK TCP algorithms with and without ENA. The results show the performance of the TCP algorithms with ENA to be superior to those without ENA.     

无线传感器网络自适应链路层FEC控制策略*

提出一种适用于无线传感器网络的自适应链路层FEC控制策略。该策略基于Kalman滤波器预测当前的网络状态,在数据链路层采用FEC控制机制,根据FEC能耗分析的自身特性自适应地调整FEC参数n,以便改善无线传感器网络的通信性能,并建立单跳无线传感器网络模型和能量模型。数学分析和仿真验证表明,该策略能够有效地提高无线传感器网络数据传输的可靠性,降低无线传感器网络的能量消耗。     

Kalman滤波的自适应链路层FEC控制策略

无线网络动态的信道特性、高误码率和带宽有限等特点,使得在无线环境下为实时流媒体传输提供QoS保证面临更大的挑战。提出一种用于无线实时流媒体传输的自适应链路层FEC控制策略,以显著提高接收方的播放质量。该策略采用跨层设计的方法,基于Kalman滤波器预测当前的网络状态,考虑物理带宽限制和GOP可解码帧数的特性自适应地调整FEC参数N;另一方面,在应用层采用自适应FEC策略,在视频源数据和冗余数据之间动态分配网络带宽。数学分析和仿真验证均表明,该策略能使接收方获得最大的可播放帧率,有效地提高了流媒体传输的可靠性和实时性。     

Improving TCP fairness and performance with bulk transmission control over lossy wireless channel

The traditional windows-based TCP congestion control mechanism produces throughput bias against flows with longer packet roundtrip times; the flow with a short packet roundtrip time preoccupies the shared network bandwidth to a greater extent than others. Moreover, the blind window reduction that occurs whenever packets are lost decreases the network utilization severely, especially in networks with high packet losses. This paper proposes a sender-based TCP congestion control, called TCP-BT. The scheme estimates the network bandwidth depending on the transmission behavior of applications, and adjusts the congestion window by considering both the estimated network bandwidth and the packet roundtrip time to improve fairness as well as transmission performance. The scheme has been implemented in the Linux platform and compared with various TCP variants in real environments. The experimental results show that the proposed scheme improves transmission performance, especially in networks with congestion and/or high packet loss rates. Experiments in real commercial wireless networks have also been conducted to support the practical use of the proposed mechanism.     

Channel adaptive video stream switching for broadband wireless links

This paper exploits an H.264/Advanced Video Coding codec’s smooth stream switching to achieve robust video delivery across an IEEE 802.16 (WiMAX) broadband wireless link. As the wireless channel conditions vary over time, dynamic selection of bitrate and corresponding video quality will reduce the risk of harmful packet loss. The paper investigates choice of stream-switching with Secondary SP-frames or SI-frames relative to the selection of quantization parameter (QP) values. To control the switching points at the WiMAX server, the proposed scheme applies a feedback mechanism that monitors packet loss. As an additional suggestion, the paper considers an adaptive ARQ scheme to protect switching frames against packet loss. In summary, the broadband wireless streaming system gives more protection to higher quality video, reduces delay and packet loss, and improves received video quality. In particular, for the QP values selected, results show that increased quality primary-switching frames together with SI frames bring a significant gain in video quality compared with other switching schemes with secondary SP-frames. The other schemes in turn show an improvement to using ‘no switching’ when streaming takes place over a typical WiMAX channel with burst errors. Link delay is also reduced.